How do I know if I'm having BH or if the babe has moved into a certain position?

I'm 23 weeks today and since about 21 weeks I've found that my stomach around my belly button, or just under it, will get really hard and it's uncomfortable. I initially thought the babe had rolled up into a funny position. I didn't think BH started this early. However I just read a poll on here that suggested BH can start as early as 22 weeks.

So do you think it's the baby or Braxton Hicks?